For an island almost smack on the equator, why are solar panels so hard to spot in Singapore? This question struck me as I endured yet another scorching day.
March to May are usually the hottest months of the year with temperatures frequently hitting 34 degrees Celsius, sometimes reaching 35 or 36. But a recent report in Today newspaper indicates that the future may be worse.
Over the past six decades, temperatures here have risen at a rate more than double that of the global average, with rapid urbanisation cited as a likely major contributing cause, the Meteorological Service Singapore (MSS) said on Tuesday (March 22).
Releasing its inaugural Annual Climate Assessment Report with a focus on last year’s climate trends, the MSS said temperatures in the Republic rose by an average of 0.25°C per decade between 1948 and last year, compared with the global increase of 0.12°C per decade between 1951 and 2012.
— Today newspaper, 23 March 2016, S’pore temperatures rising at double the global average. Link.
The Met Department pointed out that global accumulation of greenhouse gases cannot be blamed for all the temperature increases we have experienced. The relentless urbanisation of Singapore has to shoulder much of the blame. Echoing the department’s point,
Associate Professor Matthias Roth, deputy head of the National University of Singapore’s (NUS) Department of Geography, said built-up areas in Singapore have approximately doubled since the 1950s to accommodate a fast-growing population.
“As vegetation is turned into concrete and paved surfaces, the incoming energy from the sun is stored in man-made structures during daytime and released at night, thereby increasing local temperatures,” he said, adding that this “urban heat island effect” is a well-known phenomenon that also explains the trend towards warmer nights.
One evening a few years ago, I happened to be in Bukit Batok, walking from a dense cluster of housing blocks to a bus stop a few hundred metres away. It was the nearest bus stop, though it was located along a quiet road behind which was a hillside full of trees. The drop in temperature as I reached the bus stop was noticeable. I’d say it was two degrees cooler, thanks to the evaporative effect of the vegetation around the bus stop.
That said, it is unrealistic to turn the clock back. There is no way we can de-urbanise and re-forest Singapore. There is no practical way we can reduce Singapore’s population to around one million, which was what it was in the 1950s.
Yet, I don’t think we need to. Technology is there to be seized.
Granted, I don’t think there is any ready technology as of today that can reverse the “urban heat island effect”, but what I will argue here is that it is not far fetched. It may take plenty of research, which in turn requires huge funding and political will, but if we want to keep Singapore liveable, it is something we need to do. Moreover, the technology (and products) so developed can be marketed globally. Being the first to acquire the knowhow and develop it to commercial scale is an export booster.
The sun pumps out energy as electromagnetic radiation in a vast span of wavelengths. It may surprise some readers here that the human eye cannot see a good chunk of the wavelengths. Slightly less than half the sun’s energy reaches the Earth’s surface in the visible light spectrum, the rest is mainly in the infrared, which our eyes cannot detect.
However, our skin can detect infrared; we feel it as warmth.
As sunlight comes through the atmosphere, infra-red interacts with the molecules in it. It is particularly absorbed by water vapour, carbon dioxide and some other pollutants. Environments with high water vapour and carbon dioxide content will feel warmer. That’s why carbon dioxide is considered a greenhouse gas, and why in our humid climate, we’re always feeling warm.
However, with ingenuity, we should be able to discover or design other molecules that also absorb infrared radiation but with the added advantage that the material outputs electrons. In other words, it converts infrared energy into electrical energy. If we then embed these molecules into panels, what these panels will do is to soak up the infra-red from our environment. Better yet if we can embed these molecules into flexible sheets so that even non-rigid surfaces can become solar absorbers.
This is not a new idea. Scientists are already working on it. See this article: Harvesting the energy of the infrared spectrum.
I can’t find it again now, but I came across a news report on the web recently that someone has already done this. [Thanks to reader Patricia, here is a Bloomberg Business report Invisible solar cells that could power skyscrapers. It’s not the report I saw earlier, but it tells a similar story.] As you can see, proof of concept has been achieved, but the inventors are still some way from scaling it up and getting to commercial viability. If I remember the demonstration correctly, what this firm had was a film impregnated with organic molecules that not only absorbed infrared and converted it to electricity, it allowed wavelengths of visible light to pass through. In other words, the film was transparent to the human eye. You could stick it onto the outside of a glass window and get electricity without sacrificing your view. Cool eh?
Solar panels as primary material for buildings’ skins
Now stop for a moment. Imagine a cityscape dense with tall buildings like Singapore. Imagine that virtually all buildings use solar panels for their external skin. Where no windows are needed, the panels absorb both visible and infrared wavelengths. Where there are windows, the panels only absorb infrared. Rooftops are likewise chock-a-block with solar panels.
We could even think about embedding the molecule in road-surfacing material. Our roads then become ribbons and ribbons of solar-radiation absorbers.
Actually, roads already are super solar-radiation absorbers, except that currently, they absorb the infrared and get hotter and hotter. At night, the roads release the heat back to the air, making our nights warm, augmenting the urban heat island effect. The difference, when we have invented the right molecules to impregnate the road surface with, is that the absorbed infrared is converted into electricity and not into heat. After sundown, the road has far less heat to release back into the atmosphere, thus not warming our evenings (and feeding into the next day’s heat).
When solar panels have become the primary surface material for our buildings and roads, we’d be producing so much electricity, the need to burn fossil fuels for power generation should be reduced. At the very least, we shouldn’t need to go for nuclear power, official denials notwithstanding.
More to the point of this article, as efficiency improves and a higher and higher percentage of infrared is absorbed, there should be a cooling effect. All it takes is a reduction of maybe 5 or 6 degrees to make Singapore very pleasant. We’d have mornings and evenings around 22 or 23 degrees (just like in airconditioned spaces today), while dipping to perhaps 17 or 18 degrees in the early hours before dawn. Afternoons may still be warmish, with highs around 28 degrees.
One shortcoming that current technologies haven’t quite addressed is that they require direct solar radiation. Solar panels for example are virtually useless unless the sun shines almost directly on them from a single direction. The prototype infrared film I mentioned above likewise requires strong, direct sunlight to have even minimum efficiency.
For Singapore, this won’t do. Due to the persistence of cloud cover and the many ways building surfaces reflect and scatter radiation, any technology that requires direct solar radiation to work properly will fail to do a good job in our climate. For our needs, we will have to do our own research and development aimed at harvesting diffuse radiation.
Diffuse radiation is when the rays (visible or infra-red) comes to a panel or film from all sorts of directions. This is because while solar radiation arrives at Earth in essentially a straight line, once the rays hit clouds, atmospheric particles or surfaces, they bounce around. This explains how you can still see things in shadows. It is never completely pitch-black under a shed, during daytime at least.
It is a huge challenge to design solar receptors that can maintain high efficiency when the radiation reaches it at all sorts of angles. So I’m not one to underestimate how difficult it is. We’re talking about a decades-long, heavily funded national project.
Will it really lower the temperature?
I anticipate that there will be two major criticisms of this idea.
Firstly, it can be argued that before infra-red hits the surfaces, be they roads or buildings, they would have passed through our humid air and warmed it up already. So even if we empanel 100% of the surfaces, and even if they are good at extracting energy from diffuse radiation, the infra-red would have done much of its dirty work before hitting the surfaces.
How much cooling can we hope to get?
Just a little bit — is probably the answer. But just a little bit is all we need. We’re not out to create icy winters.
Consider this: By my Bukit Batok anecdote, areas dense with concrete are some 2 degrees warmer than a nearby forested environment. Globally, urban heat islands are said to be on average five degrees warmer than their rural hinterlands. In other words, if we can just counteract the heat sink effect of concrete through absorbing the infra-red that falls on it and thus reverse the urban heat island effect, we’d get a noticeable cooling already.
In any case, we should not underestimate how much direct infrared there remains even if the rays have travelled through the air. For example, when we stand in the sun, our sun-facing skin immediately protests. It feels hot. The heat isn’t only from the warmed air around us; it is a direct conversion from the infrared hitting our skin.
The second criticism is that air flows. Even if we manage to cool the air in our city, warm air from neighbouring regions may flow in.
Of course this is unavoidable. The saving grace may be that Singapore is surrounded on most sides by sea, so even if air flows in, it won’t be warmer than urban heated air. Sea breezes are normally considered welcome, are they not?
Why not just plant trees?
Why not just plant more trees? Have plenty of “green walls” – i.e. foliage on vertical surfaces. However many trees, I don’t think this solution will be enough. Trees cool by evaporation. As far as I know, chlorophyll doesn’t much absorb infrared. In other words, trees do not do the key thing we need done: withdraw infrared energy from the environment.
In any case, what are we going to do with the vast expanses of roads that absorb heat? Plant trees on them?
It’s a pipe dream
Some — correction, many — will say it’s all a flight of fancy, a pipe dream.
Yet, that’s the trouble with Singapore: we don’t dream. We mock dreaming. We dismiss ideas simply because it’s never been done before.
I’d argue that the idea is not as crazy as appears at first sight. There was a time when people thought it madness to dream about flying in a heavier-than-air machine. Today, it is routine. And not just that we can fly, but the scale of it! The size of the Airbus A380, the millions of passengers thronging airports — all a mere 110 years from the Wright brothers’ experiment.
I’d also say Singapore has a unique reason to embark on this research. We’re the biggest rich city near the equator; no place else has the same motivation to work on infrared absorption, especially diffuse infrared. Most places on earth have far more days of blue skies and direct sunlight than we do whereas we almost never have a day without clouds. However advanced other countries’ solar panels become, they may never be totally suitable for us because they are likely to focus their development efforts within conditions of direct rays. Here, we just don’t have the same reliability of direct solar radiation. We should develop our own technology, focussed on capturing diffuse radiation.
Singapore’s dreams often come up against the reality that we have a small market size. Commercialising innovations without a large home market is doubly hard. In this matter however, looking at the huge number of office and apartment blocks we put up, our domestic market is not small at all. It can be a very good proving ground for this kind of new technology. Then we can go out and conquer the world.